The primary function of some processors is to execute computer instructions. Most processors execute instructions in the programmed order that they are received. However, some recent processors, such as the Pentium® II processor from Intel Corp., are “out-of-order” processors.
An out-of-order processor can execute instructions in any order as the data and execution units required for each instruction becomes available. Some instructions in a computer system are dependent on one another because of their reference to particular registers (known as source dependency or register data dependency). Out-of-order processors attempt to exploit parallelism by actively looking for instructions whose input sources are available for computation, and scheduling them ahead of programmatically later instructions. This creates an opportunity for more efficient usage of machine resources and overall faster execution.
An out-of-order processor can also increase performance by reducing overall latency. This can be done by speculatively scheduling instructions while assuming that the memory subsystem used by the processor provides the correct data when the instruction is executed, as performed in the above-referenced parent application. However, several types of dependencies between instructions may inhibit the proper speculative execution of instructions. These dependencies may include register or source dependencies and memory dependencies. Addressing these dependencies increases the likelihood that a processor will correctly execute instructions.
Therefore, there is a need for a technique to adequately address the different types of dependencies that may prevent the proper execution of instructions in a processor.